In the commonly known way, a brush holder is mounted on the shaft of the rotor of a starter so as to make the brushes cooperate with an electric commutator integral with the shaft of the rotor. The brush holder comprises a baseplate supporting a set of cages, each serving as housing for a brush. The brushes consisting of electrically conductive material allow power to be supplied to the rotor by commutation of the electric current in the conductors of the rotor.
For this purpose, each brush comprises a face intended to rub against the conductive segments of the commutator connected to the winding of the rotor. An elastic means, such as a spring, exerts a force on each brush held in a cage in the direction of the commutator to ensure contact between the brush and the commutator segments.
The brushes have alternate polarities. Thus, the brushes of positive polarity are electrically connected, via their respective braid, to an inter-brush connector to which the feeder wire leading from the contactor of the starter is also electrically connected. In addition, the brushes intended to return current are electrically connected to the mass of the machine by means of their respective braid welded onto the baseplate.
As visible on FIG. 1, in certain configurations of brush holders, it is known to use a helical spring 1 comprising a coiled part 2 mounted on a leg 3 as well as an arm 4 extending from an end of coiled part 2 intended to rest against an end face of brush 5 opposite the face in contact with the commutator segments. To enable spring 1 to apply a force on brush 5, arm 4 passes via an opening 6 arranged in a lateral wall 7 of brush cage 8.
Due to the torque applied by spring 1 to leg 3 as well as vibrations experienced by the system, spring 1 tends to position itself transversely relative to leg 3 and rub against one of the parallel edges of opening 6 (high edge (see arrow F) or low edge depending on the operating conditions), which can cause a blockage in the displacement of arm 4 of spring 1.